Hybrid integration of photonic and electronic components provides a lower cost alternative to fully monolithic integration. Individual components can be fabricated using preferred materials and techniques and then assembled on a common substrate or carrier. Optical light guides are required for broadband interconnections between the optical and/or optoelectronic devices. To be economically viable these light guides must be low cost and easily manufactured.
As used in this specification, a light guide is a material that is at least partially transparent to light and is capable of guiding light, as for example a lens or a waveguide.
An optical waveguide is comprised of a region of high refractive index material surrounded by materials of lower refractive index. Optical waveguides have been fabricated on a variety of substrates including semiconductors, glass, Lithium Niobate and the like. They are typically formed by first preparing a low-loss planar slab and then defining the waveguide regions using one of a variety of techniques. These techniques include: (1) wet chemical etching, laser-assisted etching, or reactive ion etching (all of which remove material in specific areas to form waveguide ridges); (2) ion bombardment or ion exchange, which create a molecular disorder to alter the refractive index; (3) photopolymerization of organic polymers; (4) photobleaching of organic dyes in polymers; and (5) injection molding.
The processes described above typically require the use of a mask which contains the layout of the waveguides. Modifications to the layout therefore require the fabrication of a new mask which is time consuming and adds expense. Computer-controlled direct write systems are more suitable for rapid prototyping of optical waveguides. Several groups have reported laser writing techniques which selectively cure, through a photochemical process, waveguide regions from a film of liquid polymer [see Krchnavek et al., Laser direct writing of channel waveguides using spin-on polymers, J. of Applied Physics, vol. 66, no. 11, 1989]. These systems require that a uniform film be first deposited over the entire substrate. Following the laser writing procedure, the remaining unexposed material is removed. The dimensions of the waveguide are determined by the size of the focused spot used to cure the material. To achieve small features the light source must produce a good quality beam (near Gaussian) which can be tightly focused. This typically requires the use of an expensive UV laser source. In addition, the incident energy level of the light source must be carefully controlled in order to rapidly cure the waveguides without degrading the optical properties.